Many web publishers, both new and seasoned alike, are in the dark about getting their sites indexed in the search engines and keeping them there. While in the past webmasters were able to throw up sites with no real value and manipulate the system to get them ranked, today's landscape is vastly different.
The same "tricks" that previously worked will now get you banned faster than you can say "banned". But, now even trying to work within the misty guidelines set out by the search engines themselves can also leave you penalized and scratching your head. Over-optimization can cause your site to drop in the rankings and even disappear altogether. Look no further than Google's "sandbox" for proof of a deliberate effort to punish publishers for trying to make an end run around them with SEO work.

Incoming links were long considered a measure of a site's popularity, and the search engines regarded them as such as well. But, as publishers with dubious intentions began instituting links pages with the sole purpose of raising their site's popularity and ranking, these same links can now have a negative impact. Reciprocal links MUST have relevant sources. If your site is one that deals with pizza, links from gambling sites will only hurt you.
Some of those nefarious aforementioned "tricks" that are NOT preferred and mostly likely will get you banned:
Cloaking - Showing a version of a web page to users, and a different one to search engines with the intention of getting ranked.

Hidden Text - Repeating keywords to improve ranking in the search engines, and having those keywords be the same color as the background.
Duplicate Content - Creating multiple pages with the same content to draw in more visitors.
Doorway Pages - Pages not created for visitors but for search engines.
Redirects - Getting a web page listed under a search query that is not relevant, by redirect.
The SEO Golden Rule of one search engine: "If you attempt to get a web page ranked . for a search query that is not related to the topic of the web page then you run a high risk of having that page banned."
The one lesson in all of this is to stop relying on tactics and tricks. Return to the days of informative well-written content. Your site is there to provide some service, remember that and focus on it. As far as we are concerned, the one Golden Rule should be this: "Keep Users In Mind.